Improvements in micro-electronics have increased the demand for electrolytic cells in batteries that can be directly incorporated into electronic devices so as to produce a portable finished package, such as for example a cellular phone or a lap top computer. As improvements in micro-electronics reduce the size of the electronic device, the space allotted to a power supply within such device has likewise decreased. It is therefore important to maximize the power per unit space that a battery cell can provide.
When extremely thin or unusually shaped batteries are required, cells contained within flexible packaging have found advantages application. A cell contained within a flexible laminate package provides more efficient use of the space available within a device, in that the cell and package can assume a variety of shapes allowing the battery design to accommodate the space restrictions within the device.
A problem with cells contained within flexible packaging is that they are sensitive to temperature and over-voltage or over-current conditions. In this respect, cells within flexible packages tend to "gas-up" or "swell-up" under extreme temperatures or under extreme over-voltage or over-current conditions. Excessive heat, current or voltage can cause the liquid electrolyte within the cell to decompose into a combustible gaseous by-product. Internal pressures created by this buildup of gas may cause the flexible packaging to swell and even rupture. Still further, without a liquid electrolyte within the cell, the electrodes become resistive elements and energy provided thereto (for example by a battery charger) is converted to heat. If the electrode temperatures exceed the flash point of the hydrocarbon gases generated within the cell, the flexible packaging may rupture. While flexible packaging is less susceptible to a violent venting or catastrophic failure as compared to rigid metal or plastic containers, ruptures of the flexible packaging can damage electronic equipment in the vicinity of the cell.
The present invention overcomes this and other problems and provides a lithium ion battery having a current interrupt safety feature to prevent catastrophic failure with flexible packaging.